1. Field of the Invention
The present invention relates to a flow cell for forming an irradiation region therein, as a particle detector portion, and to a particle measurement apparatus for obtaining particle information, including a diameter of particles and so on, which are suspended in sample fluid passing through the irradiation region by using the flow cell.
2. Description of Relevent Art
As shown in FIG. 8, a conventional flow cell 100 is made of a transparent material, and is constructed to have a straight flow path or passage of a predetermined length, having a square cross-section thereof. And, an outer wall surface 101a and an inner wall surface 101b of a wall portion 101, constructing the flow cell 100 through which a laser beam La passes, are formed to be parallel each other.
Also, as shown in FIG. 9 when the laser beam La from a laser light source is irradiated upon the flow cell 100, the laser beam La is incident upon a boundary surface between air and the outer wall surface 101a at an incident angle xcex811 (xcex811xe2x89xa00xc2x0) and is refracted at an refraction angle xcex812.
This is because, when the laser beam La is incident upon the outer wall surface 101a of the flow cell 100 at right angle by setting the incident angle xcex811 to be zero (xcex811xe2x89xa00xc2x0), the laser beam La is reflected on the outer wall surface 101a, so as to return a portion of the reflection light back to the laser light source. Therefore, it is prevented from superposing on the laser beam La as return or feedback noise.
However, depending on the refractive index of sample fluid 102 (i.e., a solvent of the sample fluid) flowing inside the flow cell 100, the refraction angle of the laser beam La changes at the boundary surface between the inner wall surface 101b and the sample fluid 102, therefore the laser beam La propagating within the sample fluid 102 comes to be La1 (in a case where the refractive index of the sample fluid is n2) or La2 (in a case where the refractive index of the sample fluid is n3). As a result of this, the irradiation region M, being provided at the center of the flow passage as the detection portion of particles, is shifted in the position thereof.
Namely, according to Snell""s law, when the laser beam La is incident upon the boundary surface between the inner wall surface 101b and the sample fluid 102 at the incident angle xcex8 13 (the outer wall surface 101a and the inner wall surface 101b are parallel each other, therefore xcex813=xcex812), the refraction angle comes to be xcex814 if the refractive index of the sample fluid is n2, and it comes to be xcex815 if the refractive index of the sample fluid is n3.
Then, a light collecting means, which is provided to fit to the position of the irradiation region M corresponding to the sample fluid of refractive index n2, is shifted or not properly aligned in the position thereof in the case where the sample fluid has a refractive index n3. In such a situation, the light collecting means cannot detect light scattered by particles passing through the irradiation region M.
Accordingly, there is a problem that particle information, including a particle diameter and so on, cannot be detected accurately, due to the the difference in the kinds of sample fluids being analyzed.
Furthermore, depending on the shape of the wall portion 101 constructing the flow cell 100, the laser beam La passing through the irradiation region M is reflected on the boundary surface between the sample fluid 102 and the inner wall surface 101c and/or between the outer wall surface 101d and air, to be turned or reflected back toward the laser light source in a part thereof. Therefore, there are problems that the portion of the reflection light superposes on the laser beam La as feedback noise, and that the portion of the reflection light passes through the irradiation region M again, thereby increasing noise.
According to the present invention, for overcoming the problems mentioned above, there is provided a flow cell for obtaining particle information, including a diameter of particles and so on, suspended in sample fluid, wherein an irradiation region, through which the sample fluid passes, is defined in said flow cell for functioning as a detection portion to be irradiated with light, and a wall portion of said flow cell is so adapted and arranged that when said light is incident upon an outer wall surface of the flow cell at a predetermined incident angle xcex8 (xcex8xe2x89xa00xc2x0), said light exits from an inner wall surface into said sample fluid at a refraction angle of almost or approximately 0xc2x0.
With this flow cell and arrangement according to the invention, it is possible to keep the irradiation region functioning as a particle detection portion at a constant position, independent of and influence by a value or magnitude of refractive index of the sample fluid.
Further, according to the present invention, there is also provided a flow cell for obtaining particle information, including a diameter of particles, suspended in sample fluid, wherein an irradiation region, through which the sample fluid passes, is defined in said flow cell for functioning as a detection portion to be irradiated with light, and a wall portion of said flow cell is so adapted and arranged that said light becomes incident upon a boundary surface between said sample fluid and an inner wall surface of the flow cell at a predetermined incident angle xcex1 (xcex1xe2x89xa00xc2x0) after being passing through said irradiation region.
With this flow cell and arrangement according to the invention, after light passes through the irradiation region functioning as a particle detection portion, the light can be prevented from being reflected on the boundary surface between the sample fluid and the inner wall surface back into a direction of the light source, independent of and influence by a value or magnitude of refractive index of the sample fluid. This advantageously prevents superposing of the feedback noise onto the light due to self action a portion of the light, as well as avoiding an increase of the noise due to the portion of reflection light passing through the irradiation region again.
It is preferable that, in the flow cell as defined above, the wall portion of the flow cell is so arranged that the light is incident upon a boundary surface between an outer wall surface of the flow cell and air at a predetermined incident angle xcex1xe2x80x2 (xcex1xe2x80x2xe2x89xa00xc2x0).
With this additional feature, after light passes through the irradiation region functioning as a particle detection portion, the light can be prevented from being reflected on the boundary surface between the sample fluid and the inner wall surface into a direction of, the light source, independent of any influence by a value or magnitude of the refractive index of the sample fluid, and in addition, the light can also be prevented from being reflected on the boundary surface between the outer wall surface and air back into a direction reflected portion of the the light source, superposing of the feedback noise onto the light due to turn-back of light, as well as avoiding an increase of the noise due to the portion of reflection light passing through the irradiation region again.
Furthermore, according to the present invention, there is also provided a flow cell for obtaining particle information, including a diameter of particles, suspended in sample fluid, wherein an irradiation region, through which the sample fluid passes, is defined in said flow cell for functioning as a detection portion to be irradiated with light, and a wall portion of said flow cell is so adapted and arranged that said light becomes incident upon a boundary surface between said sample fluid and an inner wall surface of the flow cell at approximately 0xc2x0, and then becomes incident upon a boundary surface between an outer wall surface of the flow cell and air at a predetermined incident angle xcex1xe2x80x3 (xcex1xe2x80x3xe2x89xa00xc2x0) after passing through said irradiation region.
With this flow cell and arrangement according to the invention, it is possible to prevent the light from being reflected on the boundary surface between the outer wall surface and air back into a direction of the light source, thereby preventing superposing of the feedback noise onto the light due to a reflected portion of the light, as well as avoiding an increase of the noise due to the portion of reflection light passing through the irradiation region again.
And, according to the present invention, there is further provided a particle measurement apparatus, comprising: a flow cell as described above; a light source for irradiating light upon a passage of said flow cell, so as to form an irradiation region; and an optical detection process means for detecting and processing scattered light, transmission light and/or diffraction light caused by particles within said irradiation region.
With this apparatus according to the invention, it is possible to measure the number or diameter of the particles suspended in the sample fluid, independent of a value or magnitude in the refractive index of the sample fluid.